The present invention relates to improved insulated glass windows. The present invention also relates to a matrix incorporating the improved zeolite adsorbent compound. More particularly, the invention relates to the use of the improved zeolite adsorbent compound in insulated glass windows.
Zeolites are well-known adsorbents which have been used in insulated glass windows between the glass panes, either alone or within a matrix. Generally, the zeolites are disposed along the periphery of the space enclosed by the glass panes, and the zeolites adsorb water vapor from the space between the panes to prevent the formation of a fog between the panes. The zeolite functions as a molecular sieve having pores into which the material being adsorbed passes. The pores in the molecular sieve have apertures of a size sufficient to permit the molecules of the material being adsorbed to pass-through, but small enough to block materials not adsorbed. Such molecular sieve zeolites for use in insulated glass windows are disclosed in U.S. Pat. Nos. 4,151,690, 4,141,186 and 4,144,196.
Zeolites are known to have pore sizes ranging between about 3 and about 10 angstroms. Insulating glass windows generally consist of two panes of glass separated by an air space. Generally, the zeolites are placed in a channel along the perimeter of the window pane, or incorporated in a matrix around the parameter. The matrix typically comprises a polymer well-known in the art and into which the activated zeolite is bound. Zeolites with pore sizes greater than about 3, are typically used to adsorb gaseous components in the air space. These gaseous components which can be adsorbed by such zeolites include oxygen and nitrogen, as well as water and organic vapors. When the temperature rises or the pressure lowers, the oxygen and nitrogen are released from the zeolite adsorbent. This phenomenon is known as out-gassing. When these zeolites are used in a matrix between the glass panes of a window, they adsorb oxygen and nitrogen when cooled (as during the evening hours) and then release the gases when the glass is heated (as during the daytime hours). This adsorption and desorption of gases can result in pressure variations in the enclosed air space between the glass panes. Such fluctuation can lead to window problems such as excessive deflection or inflection, or window failures from excessive flexing of the seal surrounding the window edges. Such out-gassing can also lead to a loss of adhesion between the glass panes and the matrix when the matrix is cured. The loss of adhesion generally results from the formation of bubbles in the matrix which then migrate to the adhesive-to-glass surface when such gases are released by the adsorbent.
In addition to the above gases in the enclosed air space between the glass panes, there are traces of the solvent from the matrix or inserts within the panes of the window. Over the life of the window, the matrix or other internal components in the window release solvent molecules which are larger than can be accommodated by the small pore adsorbents. In an effort to capture this solvent and keep it from forming a cloud, or a xe2x80x9cchemical fogxe2x80x9d, and to prevent the chemical fog from condensing on the glass panes, a larger pore zeolite selective for the adsorption of the solvent molecules is included in the adsorbent material in the matrix or in the desiccant material.
U.S. Pat. Nos. 4,141,186 and 4,144,196 attempt to solve this problem by using zeolite adsorbents with pore sizes of about three angstroms or less in size so that oxygen and nitrogen molecules cannot enter into the pores, thus preventing the adsorption and desorption of these gases. In another patent, U.S. Pat. No. 4,151,690, it is disclosed that zeolite adsorbents with larger pore sizes can be pre-treated by adsorption of a low molecular weight polar material to partially suppress the undesirable adsorption of the gases.
U.S. Pat. No. 3,868,299 to Ulisch discloses the use of an adsorbent designed for use in multiple layer, or multi-layer, insulating glass windows comprising a small-pore zeolite in combination with a large-pore adsorbent and, optionally, a clay binder. Ulisch discloses that small-pore zeolites include sodium zeolite A, and large-pore adsorbents include faujasite, active carbon, silica gel, aluminum oxide and mixtures thereof. Kaolin, attapulgite, bentonite, waterglass, gellable silica sols and mixtures thereof are disclosed as suitable binders. Ulisch discloses that the adsorbent materials are prepared by methods known in the art as oil dropping, wherein a suspension of the adsorbent materials is stirred with an aqueous stable silica sol to form a free-flowing suspension which is subsequently introduced to a liquid immiscible with water to form droplets of the required size. The bead granulates formed are removed from the liquid as completely homogeneous bead granulates. The bead granulates are screened, dried, and dehydrated in hot air at about 350xc2x0 C. Bead granulates produced in this manner represent the most common beads for use in insulating glass windows and, typically, have bulk densities ranging from about 0.640 gm/cc (40 lbs/ft3) to about 0.960 gm/cc (60 lbs/ft3) and range in size from about 10 to about 40 mesh.
Others such as U.S. Pat. No. 4,835,130 to Box, and hereby incorporated by reference, disclose the preparation of adsorbents for use in multi-pane windows by providing a zeolite material having a mixture of at least two zeolites having a pore size of 4 angstroms and a zeolite having a pore size up to and including 10 angstroms, which has been out-gassed by heating the zeolite to drive out gases and water vapor. The zeolite material is covered with a fluid such as a paraffinic, naphthenic, or aromatic oil which is impervious to nitrogen or oxygen and the covered zeolitic material is incorporated into a sealant matrix such as butyl, resin, zinc oxide, carbon black, aromatic resin, and silane.
U.S. Pat. No. 4,476,169 relates to an adsorbent material for multi-layer glazing wherein an adsorbent in the spacers consists of a granular zeolite having a core of synthetic zeolite with a clay binder wherein the core has more zeolite than the particle as a whole, and a shell of synthetic zeolite with a clay binder wherein the shell has more clay than in the particle as a whole, and of particles of activated carbon coated with synthetic latex.
Although combinations of small pore zeolite A and larger pore zeolites such as zeolite X have been used in insulated glass windows, the problem of out-gassing from the zeolite in the matrix which leads to the accelerated failure of the insulated glass window has not been resolved. Even though attempts have been made to maximize the amount of the small pore zeolite relative to the large pore zeolite, the problem of the large pore zeolite adsorbing air as well as solvent has not been resolved. When 13X zeolite is employed in the adsorbent mixture, the insulated window out-gassing problem often results.
It is an objective of the present invention to provide an adsorbent material for use in insulated glass windows which has a reduced capacity for adsorbing selected gases from air while retaining the capacity to prevent premature failure of insulated glass windows by release of solvent molecules.
It is an objective of the present invention to provide a large pore zeolite material which has a reduced affinity for the adsorption of air when used in insulated glass windows.
It is an objective of the present invention to mitigate the out-gassing problem in insulated glass windows by reducing the amount of nitrogen adsorbed by the adsorption material using an improved zeolitic adsorbent.
It was surprisingly discovered that the nitrogen adsorption capacity of a faujasite-type zeolite in insulated glass windows can be significantly reduced by low levels of ion-exchange of the FAU-type zeolite with an alkali metal without significantly reducing the adsorption of solvents. It was discovered that the nitrogen adsorption capacity of FAU zeolite, having a silica to alumina ratio of about 2.0 to about 2.5, and particularly an X zeolite can be significantly reduced by low levels of ion exchange with an alkali metal such as potassium, wherein low levels of ion-exchange means less than about 75 equivalent mole percent exchanged. More particularly, the nitrogen adsorption capacity of the X zeolite was significantly reduced by ion-exchange with potassium at potassium levels comprising from about 5 to about 40 equivalent mole percent potassium.
In one embodiment, the invention is a process for using an adsorbent compound for use in a matrix for the fabrication of insulated glass windows wherein the adsorbent compound comprises a zeolite A in combination with a FAU zeolite which has been partially ion-exchanged with a cation comprising an alkali metal, said faujasite having a framework silica-to-alumina ratio from 2.0 to 2.5 and containing from about 0.1 to about 75 equivalent mole percent of said cation.
In a further embodiment, the invention is a process for using an adsorbent in insulated glass windows for the adsorption of water and solvent vapor wherein the adsorbent comprises a FAU zeolite having a framework silica to alumina ratio of from about 2.0 to 2.5 and containing from about 5 to about 75 equivalent mole percent alkali metal cations selected from the group consisting of potassium, lithium, rubidium and cesium and having from 25 to about 95 mole percent sodium cations, the total cation equivalency contributed by the potassium and sodium being at least about 90 percent.
The adsorbent or adsorbents employed in insulating glass windows can be any of the naturally occurring or synthetically produced adsorbents which will selectively, on the basis of molecular size, adsorb water without adsorbing oxygen or nitrogen. Typically, zeolite A, zeolite X, and mixtures thereof have been used in insulating glass windows to prevent condensation. More particularly, zeolites 3A, 4A, and 13X are preferred zeolite materials.
Zeolitic molecular sieves in the calcined form may be represented by the general formula;
Me2/nO:Al2O3:xSiO2
where Me is a cation, x has a value from about 2 to infinity, and n is the cation valence. Typical well-known zeolites which may be used include FAU-type zeolites such as faujasite, Zeolite X, and Zeolite Y. Detailed descriptions of some of the above identified zeolites may be found in D. W. Breck, Zeolite Molecular Sieves, John Wiley and Sons, New York, 1974, and are hereby incorporated by reference.
It is often desirable when using crystalline molecular sieves that the molecular sieve be agglomerated with a binder in order to ensure that the adsorbent will have suitable particle size and strength. There are a variety of synthetic and naturally occurring binder materials available such as metal oxides, clays, silicas, aluminas, silica-aluminas, silica-zirconias, silica-thorias, silica-berylias, silica-titanias, silica-alumina-thorias, silica-alumina-zirconias, mixtures of these and the like, clay binders such as attapulgite, kaolin, volclay, halloysite, sepiolite, palygorskite, kaolinite, bentonite, montmorillonite, illite, and mixtures thereof may be employed. Clay binders selected from the group consisting of attapulgite, kaolin, volclay, halloysite, and mixtures thereof are preferred. Attapulgite and halloysite are more preferred for use as a binder with the zeolite adsorbent material.
Agglomerate formation techniques employed for insulating glass windows have focused on producing a concentrated agglomerate which would meet the minimum standard set by the Insulating Glass Certification Council or other certifying agency and which pass the American Society of Testing Materials (ASTM) specifications E773 and E774 (herein incorporated by reference). The minimum standard was established that the amount of desiccant per linear foot of edge be greater than or equal to the amount used in prototype tests which were based on filling one to four sides of a hollow window spacer of fixed size and perimeter. Typically, the standard size spacer is about 0.63 cm (0.25 inch) wide by about 0.63 cm (0.25 inch) deep and the prototype window is about 35.6 cm (14 inches) by 50.8 cm (20 inches).
Type 3A molecular sieves admit and adsorb water molecules and exclude oxygen molecules and nitrogen molecules. Adsorbents for use in insulated glass windows to control condensation of water vapor and of hydrocarbons or organic sulfides on the interior surfaces of the panes are typically prepared by mixing Type 3A molecular sieve zeolite with either a silica gel adsorbent or a large pore molecular sieve. The alumina has a pore diameter sufficiently large enough to permit the adsorption of benzene molecules. Generally, the adsorbent mixtures contain a minimum of about 80 percent by mole of a Type 3A molecular sieve zeolite and a minimum about 20 weight percent silica gel. For some solvent systems, zeolite 13X is substituted for the silica gel.
In the present invention, it was surprisingly discovered that low-levels of ion-exchanging of the 13X zeolite component of the adsorbent mixture significantly reduced the tendency of the 13X zeolite to adsorb nitrogen, while not impacting the ability of the 13X zeolite to adsorb hydrocarbons. It was found that even at ion-exchange levels as low as about 5 mole percent with potassium, a significant reduction of the adsorption capacity for nitrogen occurred. Continuing to ion-exchange the 13X zeolite to levels up to at least about 40 equivalent mole percent of the available ion-exchange sites normally occupied by sodium continued to produce reductions in the nitrogen capacity. Preferably, the 13X zeolite is ion-exchanged to between from about 5 to about 40 equivalent mole percent potassium, and more preferably, the 13X zeolite is ion-exchanged to between from about 5 to about 25 equivalent mole percent potassium. Referring to a zeolite X structure, it is believed that this low level of alkali metal ion exchange replaces the sodium ions in the site III position of the supercage of the faujasite structure as described in Breck, ibid., pages 92-97 and herein incorporated by reference. When at least a portion of the site III sodium cations are replaced with alkali metal cations having a charge density less than that of sodium, the affinity for the adsorption of nitrogen is reduced. Preferably, the alkali metal is selected from the group consisting of potassium, rubidium, and cesium, and more preferably the alkali metal comprises potassium. Faujasite which has been ion-exchanged with organic cations such as ammonium and quaternary amines having similar low charge densities including ammonium, methyl amine, ethyl amine, and propyl amine as described in Table 7.7 on page 552 of Breck, ibid and hereby incorporated by reference, should also be suitable for the present invention. Nitrogen adsorption capacity tests confirmed significant reductions in the nitrogen adsorption capacity for 13X zeolite adsorbent following low-level potassium ion-exchange where the range of potassium ion-exchange ranged from about 5 to about 40 equivalent mole percent potassium. Preferably, the silica to alumina ratio of the FAU zeolite which is ion-exchanged with the alkali metal will range from about 2.0 to about 5.0. Preferably, the silica to alumina ratio of an alkali metal exchanged zeolite X will range from about 2.0 to about 2.5.